Quick forging and heat treatment schedule of molybdenum and alloys thereof



Patented Oct. 19, 1954 QUICK FORGING AN -D HEAT TREATMENT SCHEDULE OF MOLYBDENUM AND ALLOYS THEREOF Robert F. Baker, Butler, N. J"., assignor to West- I ingh'ouse Eleotric'Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania.

N Drawing. Application October 10, I951; Serial No. 250,781

6 Claims. 1

This invention relates to molybdenum and its alloys and, more particularly, to such that are ductile and methods of forging the same.

The principal object of my invention, generally considered, is to manufacture'molybdenum and alloys thereof with small proportions-of other metals such as cobalt, nickel, iron and tungsten, in order to produce material which is harder, stronger and more ductile than the usual factory product.

Another object of my invention is to forge molybdenum and alloys thereof at a proper temperature, that is, at about 1200 0., quickly by upset-forging, reducing height or thickness about 60%, annealing, and finally cooling slowly to a relatively low temperature to get hard, strong and ductile material.

A further object of my invention is' to quickforge molybdenum and alloys thereof at a temperature of about 1200 6., and finally anneal and slow cool to a relatively-low temperature to increase the hardness and strength thereof.

A still further object of my invention is to Work molybdenum andalloys thereof by a series of quick forging operations without bringing the grains to a more or less equiaxedcondition by recrystallization.

An additional" object of my invention is to forge molybdenum, effecting a reduction of 50% to 60% in height or thickness, finally annealing and slow cooling, say at a rate between 65 C. and 120 0. per hour, to a relatively low temperature in order to produce metal with the desired characteristics.

Other objects and advantages of the invention will become apparent as the description proceeds.

In my copending application, Ser. No. 259,780, filed concurrently herewith and entitled Manufacturing Ductile Molybdenum and Alloys- Thereof," I have disclosed a method of rolling molybdenum and alloys thereof in several, desirably four, steps with heating for short periods of time at about 1200 0., between each pass through a rolling mill. This rolling schedule effected a reduction in cross-sectional area of as much as 50% and gave metal with an ultimate tensile strength of about 115,000 p. s. i., with an elongation of about and more. During the reheating periods, however, I have found that some recrystallization took place, whereby some of the strength and the hardness introduced during the fabrication was lost. It was necessary to accurately control the heating time and temperature between passes in order to avoid completerecrystallization of the metal and thus lose the harden- 2'. ing effects of the previous pass or passes. However, I have-foundthat-it'was necessary to allow some recrystallizationto take place duringthe heating between rolling. passes in order toprevent breaking up of the-ingot during succeeding rolling: operations;

It has been appreciated that if it were possible to avoid this reheating between passes and to make the entire reduction in thickness or crosssection without allowing any recrystallization, greater strength would result". In rolling metals, however, the metal is not only compressed by the rollers but is subjected to tensile forces pulling it therethrough Molybdenum, when in asintered or unworked state, willwithstand compression, but will failreadily in tension, evenat working temperatures, and it is believed that these tensile stresses will cause breakingof bars during rolling some recrystallization does not take place.

In the co-pend'i'ng application of Marden and Cuthbert, Serial No; 247,652, filed September 21, 1951, and entitled Low Temperature Fabricationof'lvi'olyb'd'enum and Alloys Thereoffla method was described for working molybdenum and alloys thereofbycold compression, avoiding the application of tensile forces to themetal Also, consideration has been given to hot pressing of molybdenumand its alloys for the fabrication of special sizes andshapes. In both cases, difficulties have been encountered and the amount of deformation that maybe obtained at room temperature is limited.

In hot compression, as well as cold" compression, the two. surfaces being compressed between anvils or dies of a press are heldrigidly sothat only the center portion is deformed. The-limitations to fabricating sintered or unworked molybdenum and alloys thereofby compression alone are:

I. At room temperaturet'hemetal qultequickly becomes over stressed and the rateofd'eformation is limited and slow.

2. Portions of'theingot to be deformed are held rigidly and thus may not flow as desired.

3. The pressure required is very high, whereby large pieces require prohibitively large sized or expensive equipment.

I have discovered, however, that by forging where the hammer and the anvil are in contact with the metal for only very short periods of time, which I term Upset-forging," and where successive rapid blows are used for the deformation, and the metal facing'the hammer and anvil is allowed toflow freely between suchsuccessive blows, I am able to make the same total reduction in height in one single simple operation as compared with th multior four-pass rolling schedule of the application previously referred to. No reheating prior to final use is required, other than the stress relief treatment in the annealing and slow cooling described and claimed in the copending application entitled Ductilizing Molybdenum and Alloys Thereof, which I filed jointly with Edgar S. Byron on September 14, 1951, Serial No. 246,654.

In accordance with said joint application, the metal, after working at a temperature near and desirably not higher than 1200 C., is brought in a protective atmosphere to a slightly lower stress-relieving temperature, such as 1000 C. or between 1070 and 990 C. and held for from 1 to 30 minutes, the lower the temperature the longer the time, to get hard, strong and ductile material by stress-relief, without allowing the grains to become equiaxedby recrystallization, and then slowly cooled to about room temperature or one not higher than 700 C.

In brief, my present process consists of heating the metal and forging at such a rate that during and at the end of the forging process, the temperature is low enough and the time is short enough so that recrystallization does not take place. A small piece may be so rapidly deformed under the forging hammer that there is even an increase in temperature during the working, and a large piece may be forged so slowly that it will cool too rapidly and be fractured at the end of the operation. The rate of forging and the size of the hammer must be adjusted to the size of the piece and the conditions of operation. Since it is no longer necessary to reheat during forging, in accordance with my invention, I have found that I can work molybdenum and alloys thereof with small proportions of metals selected from the group consisting of cobalt, nickel, iron and tungsten, without recrystallization taking place, and I have been able to obtain greater strengths together with a higher degree of ductilit than has been possible by other methods of fabrication, including the multi-pass rolling schedule previously referred to.

low the preferred forging procedures disclosed with proper annealing and slow cooling to obtain stress relief without recrystallization.

It will, of course, be understood that the forging procedure must be adjusted to mechanical properties desired in the finished material, as well as the kind of material being worked on. If high ductility is desired, it must be obtained at some sacrifice in hardness and strength. If

high hardness and strength are desired, some loss of ductility is necessary.

' A specific procedure for forging molybdenum alloyed with .1% of cobalt, if high ductility and moderate strength are required, is as follows: The article is heated to a temperature of between 1200 and 1250 C. and reduced in height or thickness by from 55% to 60% by upset forging. The reason for reducing the height of the piece 50% or more is to get good hardness, strength and ductility, that is, the same as that explained in my application filed concurrently herewith and previously referred to. The rate and force of the forging should be adjusted so that the temperature of the piece remains approximately constant. Proper annealing, defined as at a rate between 60 C. and C. per hour, followed by slow cooling as above described, to about room temperature or one not higher than 700 0., results in material having from 35% to 40% elongation with an ultimate tensile strength of approximately 115,000 p. s. i.

When the same kind of material is desired having a higher strength, it is necessary to lower the temperature at which the metal is forged to say approximately 1000 C. This gives a working range between 1000 and 1250 C. The rate and force of forging is again adjusted to maintain such a constant temperature, whereupon, after working, annealing, and slow cooling, as above described, material with from 20% to 25% elongation and an ultimate tensile strength of between 125,000 and 130,000 p. s. i. is obtained. If the proportion of cobalt is increased to .2%, the strength may be increased to 135,000 p. s. i.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

By the term relatively-low temperature, I mean one below minimum visible redness, from which further slow cooling will yield only a very slight increase in ductility, say about 2% elongation as measured-in a tensile test. In other words, removal of the metal from this slowcooling furnace at visible redness or 700 C. involves a loss of not more than 10% of the duotility which might be obtained. 7

I claim:

1. The method of manufacturing ductile metal from an article of powdered particles of the group consisting of molybdenum and alloys thereof with small proportions of metal selected from the group consisting of cobalt, nickel, iron and tungsten, pressed and sintered, comprising upset-forging said article to reduce its height between about 55% and 60%, while heated to a temperature between 1,000 and 1250 0., whereby successive rapid blows are used for the deformation and the metal of the article worked is allowed to flow freely between such successive blows, heating in a protective atmosphere to a stress-relieving temperature between about 1070 C. and 990 C. for from 1 to 30 minutes, the lower the temperature the longer the time, to get hard, strong and ductile material by stress relief, without allowing the grains to become equiaxed by recrystallization, and then cooling the article at a rate between 60 C. and 120 0. per hour to a temperature not higher than 700 C.

2. The method of manufacturing ductile metal from an article of powdered particles of the group consisting of molybdenum and alloys thereof with small proportions of metal selected from the group consisting of cobalt, nickel, iron and tungsten, pressed and sintered, comprising upset-forging said article to reduce its height between about 55% and 60%, while heated to a v temperature between 1200 and 1250 0., whereby successive rapid blows are used for the deformation and the metal of the article worked is allowed to flow freely between such successive blows, heating in a protective atmosphere to a stress relieving temperature between about 1070 C. and 990 C. for from 1 to 30 minutes, the lower the temperature the longer the time, to get hard, strong and ductile material by stress relief, without allowing the grains to become equiaxed by recrystallization, and then cooling the article at a rate between 60 C. and 120 C. per hour to a temperature not higher than 700 C.

3. The method of manufacturing ductile metal from an article of powdered particles of the group consisting of molybdenum and alloys thereof with small proportions of metal selected from the group consisting of cobalt, nickel, iron and tungsten, pressed and sintered, comprising upset-forging said article to reduce its height more than 50%, while heated to a temperature between 1000 and 1250 0., whereby successive rapid blows are used for the deformation and the metal of the article worked is allowed to flow freely between such successive blows, heating in a protective atmosphere to a stress-relieving temperature between about 1070 C. and 990 C. for from 1 to 30 minutes, the lower the temperature the longer the time, to get hard, strong and ductile material by stress-relief, without allowing the grains to become equiaxed by recrystallization, and then cooling the article at a rate between 60 C. and 120 0. per hour to a temperature not higher than 700 C.

4. The method of manufacturing ductile metal from an article of powdered particles of the group consisting of molybdenum and alloys thereof with small proportions of metal selected from the group consisting of cobalt, nickel, iron and tungsten, pressed and slntered, comprising upset-forging said article to reduce its height more than 50%, while heated to a temperature of about 1000 CL, whereby successive rapid blows are used for the deformation and the metal of the article worked is allowed to flow freely between such successive blows, heating in a protective atmosphere to about the same stressrelieving temperature higher than 990 C. for an appropriate period of time, the lower the temperature the longer the time, to get hard, strong and ductile material by stress-relief, without allowing the grains to become equiaxed by recrystallization, and then cooling the article at a rate between 60 C. and 120 C.- per hour to a temperature not higher than 700 C.

5. The method of manufacturing ductile metal from powdered particles of the group consisting of molybdenum and alloys thereof with small proportions of metal selected from the group consisting of cobalt, nickel, iron and tungsten, comprising pressing the particles to a desired shape, heating the pressed shape in a protective atmosphere until the particles are sinterecl into a strong coherent article, upset-forging said article to reduce its height more than 50%, while heated to a temperature between 1000 and 1250 0., whereby successive rapid blows are used for the deformation and the metal of the article worked is allowed to flow freely between such successive blows, heating in a protective atmosphere to a stress-relieving temperature between about 1070 C. and 990 C. for from 1 to 30 minutes, the lower the temperature the longer the time, to get hard, strong and ductile material by stress-relief, without allowing the grains to become equiaxed by recrystallization, and then cooling the article at a rate between 60 C. and 120 C. per hour to a temperature not higher than 700 C.

6. The method of manufacturing ductile metal from powdered particles of molybdenum, comprising pressing the particles to a desired shape, heating the pressed shape in a protective atmos phere until the particles are sintered into a strong coherent article, upset-forging said article to reduce its height between about and while heated to a temperature between 1000 and 1250 C., whereby successive rapid blows are used for the deformation and the metal of the article worked is allowed to flow freely between such successive blows, heating in a protective atmosphere to a stress-relieving temperature between about 1070 C. and 990 C. for from lto 30 minutes, the lower the temperature the longer the time, to get hard, strong and ductile material by stress relief, without allowing the grains to become equiaxed by recrystallization, and then cooling the article at a rate between 60 C. and C. per hour to a temperature not higher than 700 C.

References Cited in the file of this patent Treatise on Powder Metallurgy, by Goetzel, vol. 1, pp. 666-669, 1949. Copy in Div. 3.

Preprint 89-30 of the Electrochemical Society, pp. 377-344. Published in 1946. Copy in 148- 11.5. 

1. THE METHOD OF MANUFACTURING DUCTILE METAL FROM AN ARTICLE OF POWDERED PARTICLES OF THE GROUP CONSISTING OF MOLYBDENUM AND ALLOYS THEREOF WITH SMALL PROPORTION OF METAL SELECTED FROM THE GROUP CONSISTING OF COBALT, NICKEL, IRON AND TUNGSTEN, PRESSED AND SINTERED, COMPRISING UPSET-FORGING SAID ARTICLE TO REDUCE ITS HEIGHT BETWEEN ABOUT 55% AND 60%, WHILE HEATED TO A TEMPERATURE BETWEEN 1,000* AND 1250* C., WHEREBY SUCCESSIVE RAPID BLOWS ARE USED FOR THE DEFORMATION OF METAL OF THE ARTICLE WORKED IS ALLOWED TO FLOW FREELY BETWEEN SUCH SUCCESSIVE BLOWS, HEATING IN A PROTECTIVE ATMOSPHERE TO A STRESS-RELEIVING TEMPERATURE BETWEEN ABOUT 1070* C. AND 990* C. FOR FROM 1 TO 30 MINUTES, THE LOWER THE TEMPERATURE THE LONGER THE TIME, TO GET HARD, STRONG AND DUCTILE MATERIAL BY STRESS RELIEF, WITHRECYSTALLIZATION, AND THEN COOLING THE ARTICLE AT A RATE BETWEEN 60* C. AND 120* C. PER HOUR TO A TEMPERATURE NOT HIGHER THAN 700* C. 